“Cannot read property 'getElementsByTagName' of undefined” ERROR

I want column 5 to get the sum of "TxToplamNet" id inputs.

I would like to write the value of the column number 4 with the value of column 5 and write to the input of "Total Kdv" id.

I get a Cannot read property 'getElementsByTagName' error.

function Hesapla(Satir) {
  var Tablo;
  var SatirId;
  var Miktar;
  var Fiyat;
  var KdvOrani;
  var Tutar;
  var ToplamSatir;
  var ToplamNet;
  var ToplamKdv;


  Tablo = document.getElementById("FaturaDetay");
  SatirId = Satir.parentNode.parentNode.rowIndex;
  Miktar = parseFloat(Tablo.rows[SatirId].cells[1].getElementsByTagName("input")[0].value);
  Fiyat = parseFloat(Tablo.rows[SatirId].cells[3].getElementsByTagName("input")[0].value);
  Tutar = Miktar * Fiyat;
  Tablo.rows[SatirId].cells[5].getElementsByTagName("input")[0].value = Tutar.toString();

  try {
    for (var i = 1; i < Tablo.rows.length; i++) {
      ToplamNet += parseFloat(Tablo.rows[i].cells[5].getElementsByTagName("input")[0].value);

      KdvOrani = parseFloat(Tablo.rows[i].cells[4].getElementsByTagName("input")[0].value);

      ToplamSatir = parseFloat(Tablo.rows[i].cells[5].getElementsByTagName("input")[0].value);

      ToplamKdv += ToplamSatir / 100 * KdvOrani;
    }
  } catch (Hata) {
    alert(Hata.message)
  }

  document.getElementById("TxToplamNet").value = ToplamNet;
  document.getElementById("TxToplamKdv").value = ToplamKdv;
  document.getElementById("TxToplamGenel").value = ToplamNet + ToplamKdv;

}

<tbody>
  <tr>
    <td>
      <input id="StokAd" class="form-control form-control-sm text-left">
    </td>
    <td>
      <input id="Miktar" class="form-control form-control-sm text-right" value="0">
    </td>
    <td>
      <input id="Birim" class="form-control form-control-sm text-left">
    </td>
    <td>
      <input id="Fiyat" class="form-control form-control-sm text-right" onkeyup="Hesapla(this)" value="0">
    </td>
    <td>
      <input id="Kdv" class="form-control form-control-sm text-center" value="18">
    </td>
    <td>
      <input id="Tutar" class="form-control form-control-sm text-right" value="0" readonly>
    </td>
    <td>
      <a class="btn btn-sm btn-outline-danger" onclick="SatirSil(this)">X</a>
    </td>
  </tr>
</tbody>